Apparatus for regulating the temperature of gases containing so3 and h2so4



Nov. 7, 1933.

L. GILLETT 1,934,419

APPARATUS FOR BEGULATING THE TEMPERATURE OF GASES CONTAINING S03 AND H2504 Original Filed March 29, 1926 1 ff I l, 1

\\\\\ T//f Z0 58 k 3e j I f LowRY GILLETT 35. 3/ INVENTOR 2T 9- am' ATTORN EY Patented Nov. 7, 1933 UNITED STATES APPARATUS FOR REGULATIN'G THE TEM- PERATURE OF GASES CONTAINING S03 AND HzSOi Lowry Gillett, Syosset, N. Y., assigner to General Chemical Company, New York, N. Y., a corporation of New York Original application March 29, 1926, Serial No. 98,162, now Patent No. 1,832,482. Divided and this application June 22, 1928.

9 Claims.

This application is a division of my application Serial No. 98,162 led March 29, 1926, Patent No. 1,832,482, Nov. 17, 1931.

The invention relates to means for regulating the temperature of gases containing sulphur trioxide or sulphurc acid, particularly such gases as are employed in the manufacture of sulphuric acid. The principal object of my invention is to prevent the formation or condensation of sul- 10 phuric acid on the walls or other surfaces of the heat exchangers or transierrers employed in dry cooling the gases in the above mentioned process, which condensation results in the destruction of the apparatus and contamination of the catalyst. Another object of my invention is the provision of an improved cooling apparatus whereby increased efficiency in the cooling operation is obtained over those systems proposed heretofore for the elimination of the above mentioned condensation of corrosive acid.

In the treatment of gases containing sulphur triox'ide generally, it is of course highly desirable to Yprevent the condensation of sulphuric acid, which Will cause corrosion. This is particularly true when subjecting the gas to` dry cooling in contact with a cooling surface or heat transfer wall corrodible by sulphuric acid, as occurs in the pipe lines, coolers and heat exchangers of the system. Acid which has been once condensed does not vaporize again until the temperature is subsequently raised considerably above that at which it will initially condense. The condensed acid collects at points in the system, corrodes the equipment, particularly if steel, forming sulphates as iron sulphates, which may later become powdered and be carried along in the gas stream into the catalyst chambers, resulting in contamination of the catalyst and loss of conversion eciency. Moreover, as iron sulphate is a relatively poor conductor of heat, any sulphate which forms on the heat transfer surfaces, and is retained there, will form an insulating layer and prevent the efcient exchange of heat through the said surfaces. By operating in accordance with my invention, this objectionable condensation is eiectively prevented and a heat transfer eiiiciency obtained much greater than that which has been considered possible heretofore when operating under conditions such that no corrosion is obtained.

The objectionable presence of condensed acid in sulphuric acid systems has been long recognized and methods have been devised to prevent the formation of such condensed acid. It has been considered necessary in the past to Serial N o.

maintain the temperature of gases -in systems containing sulphur trioxide above about 400 F. in order to eliminate the possibility of condensation of sulphuric acid. This condition has been considered to be necessary irrespectiveof the composition and moisture content of the gases to be cooled, and corrosion has been found to result whenever this precaution was not observed. I have discovered that While this condition is true in some cases, corrosion Willnot always be obtained, even if the temperature of the gases is lowered to below 400 F., provided certain conditions, referred to later, are maintained.

It has been proposed to maintain the temperature of the gases undergoing cooling above that value at which it was thought that condensation of sulphuric acid from the gases would rst commence, e., about 400 F., by the use of a cooling medium preheated to this temperature. This of course means that in many cases an efficient heat transfer could not be obtained, as compared with the use of a cooling medium having a lower temperature. I have discovered reasons why this highv temperature was considered necessary and have devised a method and apparatus whereby in many instances a more efncient heat transfer and desired temperature conditions may be obtained without resulting corrosive action upon the equipment.

Other objects will appear from the following description, and by reference to the accompanying drawing, forming a part hereof, and wherein a satisfactory and typical example of an apparatusV involving my invention is illustrated. In said drawing, Fig. l is a diagrammatic elevation partly in section of a converter-transferrer column, and Fig. 2 is a plan View of the structure shown in Fig. 1.

The converter-transferrer column A as shown consists of a number of superimposed sections or compartments, of which the uppermost section B and the lowermost section D as Well as the middle compartment C constitute catalytic converters in which the catalytic material (such as platinized asbestos) is supported in any wellknown or approved manner. Between the converter compartments B, C and D respectively are interposed compartments E and E' respectively which contain heat-transferring or exchanging apparatus for the purpose-of cooling the gases on their Way from one converter section to the next. In the embodiment illustrated, each of the heat transferrers E and E' is of the same construction, although the transferrer F could be smaller because of the smaller amount of heat generated by the reactions within the converter section C, and as shown comprises a plurality of tubes 10 extending between and having their ends connected to the tube plates 11 and 12. Each of the tubes l0 preferably has mounted therein a helical baille 19 to cause the gas passing through said tubes to flow with a whirling motion and thereby ensure contact of substantially all of the gas with the cylindrical cooling surfaces of the tubes. The gases to be treated in the column A, (for example a mixture containing from 7% to 12% of SO2) are admitted through the inlet 20 at the top of the column and fiow successively through the sections B, E, C, F and D, the sections B, C and D as heretc fore pointed out, containing the catalytic material, the converter section D being provided with an outlet 2l through which the gases pass to the pipe 22 leading to the usual absorbers. The temperature of the gases entering the inlet 20 is approximately 750 F. and during this passage through the converter section B, the well-known exothermic reactions which take place therein result in increasing the temperature of the gases to about 1050 F. In passing through the heat transferrer E, the gases are cooled to the original admission temperature, a heating and cooling of the gasesalso occurring in the converter section C and transferrer F respectively. If coid air is admitted to the transferrers, the chilling `of the walls of the tubes l0 results in the condensation and formation of sulphuric acid on such walls, which acid attacks and soon destroys the metal of the tubes thereby necessitating the frequent renewal of such tubes.

According to my invention the air, or other cooling medium used, is admitted to the transferrers at a temperature of from about 200 to 400 F., and the apparatus for supplying the cooling air is so constructed that the temperature of the air can be readily controlled to maintain it between the desired limits. For this purpose each of the transferrers has secured thereto the pipes 25 and 26 preferably constructed as bustle pipes which are secured to and extend substantially half way around the circumference of the compartment, the inlet pipe 25 being located at the bottom and the outlet pipe 26 at the top and upon the opposite side of the compartment. This construction provides a counter flow of the cooling medium which of course vgives greater efficiency and is preferable to an arrangement in which the cooling medium and gas to be cooled, flow in the same direction. Communication between the pipes 25, 26 and the compartments E and F is established through a plurality of apertures 27 provided in the side wall of the column section and the flow of the air is counter to the gas flow in the tubes 10 in order to obtain the most efficient heat exchange, although ofcourse this is not essential. Preferably, a baiile 23.is interposed between the apertures for the inlet and outlet pipes to also cause a transverse flow of the cooling air. The arrangement of the bustle pipes 25, 26 is the same for each of the heat transferrers E and F and the outer ends of the pipes 25 are connected by the the outlet pipes 26. Each of the branch pipes 26a is provided with a damper 33 for regulating the air flow. Cold air is admitted to suction pipe 31 between its ends through an inlet 34, the opening of which is controlled by a shutter 35, and a damper 35 is located adjacent to said inlet to check the flow through said pipe 31. Air inlet 34 is preferably located between damper 36 and inlet of the blower. A purge pipe 37, controlled by a damper 38 and leading to any conveniently located discharge stack, is connected with the suction line between the bustle pipes 26 and the blower inlet.

It appears that when using undried air as a source of oxygen for the production of sulphur dioxide for use in a sulphuric acid system, the moisture content of the gases will frequently be in the neighborhood of 0.5 grams H2O per cu. ft. rihis moisture 'will combine with the sulphur trioxide often present in sulphur dioxide gases which have been produced by combustion of brimstone or pyrites, and if the temperature falls below about 400 F. will condense out and corrode the equipment. Likewise, when cooling the gasafter it has passed through one or more of the converters and is almost wholly in the form of sulphur trioxide, condensation will occur if the temperature drops below 400 F. As in every case the amount of sulphuric acid formed will be over five times the amount by weight of excess moisture present. in the system, and as the total amount of moisture introduced into the system is quite large owing to the large volume of air required, it can readily be seen that the problem presented is a serious one. It is common practice at present .in the production of sulphuric acid to dry the air used for oxidation before admission into the sys tem. However, it has still been considered necessary to mail tain the temperature of the gases in the system above about 400 F. while in contact with corrodible metal surfaces in order te prevent corrosion of the equipment. I have discovered that a definite relation exists between the amount of moisture in the gases and the temperature to which they may be cooled before condensation of the sulphuric acid takes place. For instance, with gases produced from undried air and containing about 0.5 grs. of H2O per cu. ft., the temperature must be maintained above about 400 to prevent condensation. However, if the air used is comparatively dry, as is frequently the case in the winter, or is rst dried to an extent such that its moisture content is down to between 0.05 and 0.1 gr. of H2O per cu. ft., I have found that the temperature may be dropped to about 300 F. before condensation will commence. If an H2O content of about 0.01 gr.-H2O per cu. ft. is maintained, the temperature may be dropped to about 240 F. before condensation will commence. When using 98% sulphuric acid Yas a drying agent, by means of which moisture contents as low as .001 to .005 may be obtained, I have found that the temperature may be dropped to approximately 200 F. and still not obtain a corrosive action upon the equipment. It will be seen, therefore, that a definite relation exists between the amount of moisture in the gases and the temperature to which they may be cooled.

It will be appreciated that this discovery permits a much more efficient cooling of gases in the system than is possible when the cooling medium is maintained at a temperature above 400 F. The temperature differential between the hot gases and cooling medium will be increased, thus permitting a more rapid abstraction of heat. The volume of cooling medium required to be circulated through the system will be smaller due to its capacity to absorb a greater amount of heat. As the size of the blower or other means for circulating the cooling medium is directly proportional to the volume of gas handled, it will be seen that not only may the heat exchangers or coolers be reduced in size, but also the blower, thus materially reducing equipment charges.

In the past, even when the exit temperature from the heat transferrers of gases, containing sulphur trioxide, was maintained above Li00 F., it was frequently found that corrosion occurred vin the equipment. The explanation for this was diiicult to see in that this temperature was fre- ,quently above the condensation temperature of sulphuric acid, even with a moisture content in the cooled gases corresponding to the use ofundried air. I have concluded that the cause of this corrosion was the formation of sulphuric acid due to localized cooling of the heat transfer surface by the cooling medium at the points of entry of the cooling medium into the heat transferrers. This sulphuric acid when once formed, does not readily Volatilize again until the temperatures are later raised to a point considerably above the condensing temperature. vAmounts of sulphuric acid would thus form at points in the heat transferrers,xcause corrosion, and necessitate repair or removal of the entire unit. I have discovered that in order to prevent this localized cooling at ,the point of entry of cooling gases into the heat transfer system, such gases must be preheated to a temperature such that the heat transfer surfaces will not be below the condensation temperature of sulphuric acid for the particular moisture content of the said sulphur trioxide containing gases. This temperature, however, may still be far below that heretofore considered necessary, especially when operating with dried air as is now common practice. It will be observed that the essential element of my invention is not only to maintain the cooled gases at their point of exit from the heat transferrers above the condensation temperature of sulphuric acid corresponding to their moisture content, but also to maintain the cooling medium at its point of entry into the heat transfer system, and at all points in the system adjacent heat transfer surfaces above this condensation temperature. This procedure eliminates entirely the condensation of acid at all points. To carry out this improved process in the most eicient manner I have devised the apparatus described herein, in which the inlet temperature of the cooling medium may be maintained at a definite value without the use of auxiliary preheaters and without added fuel cost.

The operation of the apparatus which I have devised as a means of carrying out my improved process is as follows: Gas is introduced through the inlet 2O into the column and cws successively through the compartments B, E, C, F and D. The blower 29 is put in operation, the shutter 35 and damper 36 being opened so that the air will circulate in a closed path through the heat transferrers E and F until the temperature of the air is raised to the desired temperature. If the temperature tends to rise further the shutter 35 is opened to admit cold air and thereby 1naintain the temperature between the desired limits, it being understood that the damper 38 controlling the purge pipe 37 is also opened to discharge the excess air.

During the operation, the shutter 35 and damper 38 are manipulated as required to control the temperature of the air, while the dampers 33 for the bustle pipes for each of the heat transferrers E and F may also be regulated as required to control the volume of air passing through each compartment.

It will be seen that when operating in accordance with my invention, as the temperature of the cooling medium used is lowered more than has been thoug.-t possible heretofore, a consequently smaller quantity of cooling medium is required for the abstraction of the given amount of heat. This results in lower operating costs and in lowered cost of equipment for the initial installation. A much more efficient control of the heat transfer operation becomes possible because the temperature differential existent between the hot gases andthe cooling medium is consequently greater than in prior practice.

It is of course obvious that my invention is applicable to the use of cooling mediums other than air, as for instance in those systems in which the SO2 gases are preheated to the temperatures required for conversion by passage lthrough. heat transferrers in heat transfer relation to the hot gases issuing from the conversion stages. In this case the SO2 gas after being heated in the heat transferrers would not be discharged to the atmosphere as when using air, but would be passed to the converters.

While I have illustrated in the accompanying drawing a preferred form of apparatus for carrying out my invention in connection with a multi-stage converter system, in which close control of temperature conditions is essential, and in which corrosion is highly deleterious not only to the heat transfer apparatus but also to the catalyst used in the conversion stages, it is of course clear that my invention is not confined to this particular use but is of value in connection with regulating temperature conditionsand the treatment of gases containing sulphur trioxide generally.

While I have shown the inlet and outlet pipes connecting with the transferrers as terminating in bustles, it will be understood that the invention is not limited to the use of such bustle pipes. It will also be understood various other changes and modifications may be resorted to without departing from the spirit of my invention.

I claim:

l. An apparatus of the character set forth comprising a plurality of converters connected in series, means for passing a gas through said converters7 a heat transferrer interposed between two successive converters, means for preheating a cooling medium other than the gas treated in said converters, and means for circulating said preheated cooling medium through said heat transferrer.

2. An apparatus of the character set forth comprising a plurality of converters connected in series, a cooler interposed between two successive converters and means including a blower and connections therefrom tosaid cooler to circulate a cooling medium through said cooler in a closed path.

3. An apparatus of the character set forth comprising a plurality of converters connected in series, a cooler interposed between two successive converters and means including a blower and connections therefrom to said cooler to circulate a cooling medium through said cooler in a closed path, said connections being provided with an outlet and an inlet to permit the discharge and admission of cooling medium from and to said closed path and means to regulate the amount of cooling medium discharged and admitted.

4. An apparatus of the character set forth comprising a plurality of converters connected in series, a plurality of coolers arranged in alternation with said converters, means including a blower and connections therefrom to said coolers to circulate a cooling medium in a closed path through said coolers, said means being provided with an inlet and outlet for admitting and discharging the cooling medium to and from said path, means to regulate the extent of opening of said inlet and outlet, and valves for controlling the amount of cooling medium circulated through each of said coolers.

5. An apparatus for the catalytic conversion of sulphur dioxide to sulfur trioxide comprising a converter adapted to permit the passage of sulphur dioxide containing gas therethrough, a cooler connected with the inlet of said converter, for cooling the gas entering said converter, said cooler having a passageway for cooling air therethrough, means for circulating a stream of air through said cooler in a closed path, means for permitting the escape of heated air from said closed path, and means for admitting fresh air to' said closed path, whereby the temperature of the stream of cooling air may be controlled.

6. An apparatus of the character set forth cornprising a plurality of vertically aligned converters connected in series, a cooler interposed between two successive converters and means including a blower and connections therefrom to said cooler to circulate a cooling medium through said cooler in a closed path, said connections being provided with an outlet and an inlet to permit `the discharge and admission of cooling medium from and to said closed path and means to regulate the amount of cooling medium discharged and admitted.

7. An apparatus of the character set forth comprising a plurality of converters connected in series, a plurality of coolers arranged in lalternation with said converters, the converters and the coolers being arranged in Vertical alignment, means including a blower and connections therefrom to said coolers to circulate a cooling medium in a closed path through said coolers, said means being provided with an inlet and outlet for admitting and discharging the cooling medium from said path, means to regulate the extent of opening of said inlet and outlet, and valves for controlling the amount of cooling medium circulated through each of said coolers.

8. An apparatus for cooling gases comprising g a conduit for heated gases to be cooled, means'for maintaining a stream of cooling medium in heat transfer relation with the gases in the conduit, means for permitting the escape of a portion of the cooling medium of said stream whichhas become heated, and means for admitting to` and admixi'ng with the remaining Vportion of the heated cooling -inedium of said stream, coolingm'edium entering the apparatus. i

9. An apparatus of the character described comprising a conduit" for heated gases to be cooled, a second conduit for circulating a cooling medium in heat transfer relation withgases in said first conduit, lmeans for circulating the cooling edium through said second conduit whereby said cooling medium becomes heated, means'for permitting the escape from the second conduit of a portion of said heated cooling medium, and means for admitting to said second conduit a quantity of entering cooling medium whereby the entering cooling vmedium becomes admixed with the portion of heated cooling-medium remaining in the second conduit and whereby `the 'entering cooling 'medium is preheated.

LOWRY 

